As is well known in the art of depilation, light energy can be used to destroy the hair follicle, but must be of sufficient magnitude and frequency. For example, although light emitting diodes (LEDs) deliver optical energy, the energy is continuous wave with low magnitude and is insufficient to destroy the hair follicle. Instead, LED is used for skin rejuvenation. Hair removal is done with intense pulsed light (IPL) or pulsed laser energy. The optical energy currently used in the prior art to destroy hair follicles is usually delivered in very short pulses, e.g., tens of milliseconds, so that the energy can penetrate through the skin to the follicle.
Light energy that causes thermal destruction of the hair shaft and follicle is in the range of wavelengths that are specifically absorbed by the pigment melanin found in the hair follicle, also referred to as selective photothermolysis. However, a known problem is that the epidermis through which the light energy must penetrate is rich in melanin and therefore absorbs a major portion of the energy, resulting in inadequate heating of the hair follicles as well as damage to the epidermis. Using higher energy levels in order to generate sufficient heating of the hair follicles can cause charring and hyper-pigmentation. It is known that high energy used on dark skin with either IPL or lasers can create burns.
Another problem with selective photothermolysis is that the wavelength may be insufficient for penetration deep enough to reach the target due to tissue scattering which depends on wavelength. Various techniques have been used or proposed to assist in improving the efficiency of the process. These techniques include cooling of the treated area before or during application of the light energy, or focusing techniques aimed at focusing the optical energy at a specific depth under the skin surface, so as to increase the energy fluence at that depth.